People often ask me why it is that I care so much about the nationâÄôs housing and transportation issues. In response, I ask them to consider some of the most important problems facing the nation today. Near the top of any such list would be the economic recession, energy dependence, global warming, the healthcare crisis, the wars in Iraq and Afghanistan.

I argue that all of these problems are closely connected to the way American cities were designed. The United States is the most car-dependent, suburbanized nation in the world. The most effective way to address these myriad problems will be to understand the previous mistakes of our urban design policies.

The most fundamental problem with the suburbs is that they are inefficient. The spatial distance between people means that it takes more time and more energy for people to stay connected in the physical world, whether that means a longer commute to work  or longer trips to the grocery store. This adds up over time.

This inherent inefficiency of suburbs that requires more resources to do the same work of connecting people to one another means that suburban residents cause a lot of waste. They consume more gasoline because they need to travel further and buy more cars because they seldom have alternatives.

Suburbs also require more infrastructure; they require more roads, more sewer lines, more electricity lines, more everything. Every business or government decision that caters to the suburbs is likewise more expensive.

The existence of suburban and exurban communities is predicated on the abundance of cheap fuel, meaning gasoline. The suburbanization of America therefore has huge implications for our foreign policy. Many of our military expenditures are directed toward maintaining this cheap energy supply that suburban lifestyles require.

Our various wars, occupations, and military presence in the Middle East have cost us trillions. ItâÄôs true that some of this was spent in reaction to terrorism, but then we need to ask why weâÄôre targets of terrorism in the first place. ItâÄôs certainly not because Muslims âÄúhate us for us for our freedom,âÄù as weâÄôre sometimes told. The real reason is that itâÄôs a reaction to our imperialist occupation policies, policies that exist in large measure because Americans, especially those in suburbs, demand cheap gasoline.

Besides making the wider world a more dangerous place, suburbs are themselves more dangerous than cities. It may seem counterintuitive to say that suburbs are dangerous; many people move to the suburbs precisely because they consider them a haven of safety. However, this idea is based almost entirely on perceptions of crime, and fails to take other factors into account. Consider, for instance, that more than 40,000 Americans die in car accidents per year and that suburban residents do vastly more driving than residents of cities do. In contrast, the CDC reported 18,361 homicides in 2008.

Many people assume that suburban growth is simply an outcome of the free market. Nothing could be further from the truth. The suburbs have grown as a result of vast subsidies.

A study released earlier this year by the U.S. Public Interest Research Group found that since 1947, the amount of money the government spent building and maintaining highways, roads, and streets has exceeded the amount raised by all âÄúuser feesâÄù combined, including gasoline taxes, toll roads, and motor vehicle taxes.

Today, these user fees comprise less than half of construction and maintenance expenses for the nationâÄôs roadworks. That doesnâÄôt even take into account the hidden costs on health and the environment caused by the pollution from driving.

A second way suburbs are subsidized is through whatâÄôs known as the mortgage income tax deduction, which some have dubbed the âÄúmansion subsidy.âÄù This subsidy allows homeowners to deduct their home mortgage interest from the income taxes, which incentivizes building bigger houses, the room for which only exists in the suburbs.

Estimated at $100 billion annually, the mansion subsidy remains larger than the entire annual budget of the Department of Housing and Urban Development.

Mortgages are also heavily subsidized through federal insurance policies.

The solution to these problems will not be easy. Our cities and highways have been built around the car; it will not be easy to replace them. However, we at least need to stop digging and stop the damage that the suburbanization of America is causing. We must end the policies that encourage the growth of sprawl. New developments must adapt to the new circumstances.